The present invention generally relates to vehicle tires and, more specifically, to a non-pneumatic vehicle tire.
Tires currently used on vehicles are generally pneumatic tires. With such tires, internal air pressure is necessary to carry the load acting on the tires. Vehicle tires working with internal air pressure function well in practice, however, they do suffer from significant drawbacks. Such drawbacks include complex structural designs as well as safety issues in the event of a puncture during their use on public roads.
Airless or non-pneumatic tire designs exist in the prior art. For example, U.S. Pat. No. 1,610,238 to Benson discloses an airless vehicle tire in which arcuate or C-shaped springs are disposed radially around the tire. A ring-shaped wire spring running around the circumference of the tire is threaded through loops formed in the portions of the C-shaped springs situated in the crown portion of the tire. The ends of the C-shaped springs are bent into rings in the bead portions of the tire. A pair of ring-shaped springs, each of a diameter identical to that of the bead of the tire, are threaded one each through the rings on the ends of the C-shaped springs.
Similar radially-situated leaf springs are described in U.S. Pat. No. 1,113,036 to Mitchell. The C-shaped leaf springs in this solution, however, do not contain a loop on the crown portion of the tire.
According to U.S. Pat. No. 1,471,580 to Walton, springs prepared from wires of circular cross-section are formed in two symmetrically situated semi-circles and disposed radially within the tire so that a tunnel-like arrangement is formed. Both ends of each spring are provided with a fold-back in the form of a circle. Steel wires, which play the role of the bead-rings, are threaded through the circle-shaped fold-backs. In the circumferential direction, the radial springs are tied-up in pairs by a reinforcement in the crown portion of the tire. In this solution, the tire is pressurized to ensure the necessary loadability.
The disadvantage of the above prior art tires is that each is unsuitable for carrying loads over approximately 450 lbs. as the crown portions of the springs of each become flat, and, due to the large deformation, the springs fatigue and break. Another drawback of the vehicle tires of such construction is that they can be used only on vehicles with low traveling speeds (maximum 25-35 mph). In case of larger load or speed, the temperature of the vehicle tires significantly exceeds the acceptable temperature limit of 175-195° F. due to large spring deformations. As a consequence, the rubber material ages very quickly becoming thereby unsuitable for further use. A further disadvantage of the above prior art tires is the small side stability characteristic for their high profiles. This makes their safe operation in today's high-speed vehicles impossible.
The object of commonly assigned U.S. Pat. No. 6,374,887 to Subotics is a non-pneumatic vehicle tire reinforced by arch-shaped leaf springs, preferably made of a material such as steel, that are radially disposed within the tire. The tire features a crown portion containing the running surface and two side walls joined to the crown portion via shoulder portions. The two sidewalls end in beads which are clamped into a wheel rim. The crown portion, sidewalls and the beads are kept together by ribs made of an elastic material, which are supported by the arched leaf springs. The ends of the leaf springs are embedded flexibly into the beads, and the whole vehicle tire is mounted onto the wheel rim in a pre-stressed state.
A disadvantage of the non-pneumatic tire of the Subotics '887 patent, however, is that the strengthening ribs slip on the leaf springs during functioning, since the leaf springs are not built into the rubber body of the tire. The friction thus generated results in heat generation. A consequence of this is a significant heating-up of the tire during use. Furthermore, owing to the flexible embedding of the leaf spring ends into the beads, the tire beads also heat up significantly during operation due to the large deformation of the tires. In addition, under a high loading of the tires, the spring ends are pressed into the rubber material of the beads. As a result, the bead ends of the springs move away from each other and fold-like peak deformations are generated on the crown portion of the springs. These peak deformations result in breaking of the springs after only a short time of operation.
Accordingly, it is an object of the present invention to provide a non-pneumatic vehicle tire of high wear resistance, loadability, speed and side stability, eliminating, or at least reducing, the above disadvantages of known vehicle tires.
These and other objects and advantages will be apparent from the following specification.